Menahot, Chapter Twelve, Mishnah Five
1) One may offer wine but not oil, the words of Rabbi Akiva.
a) But Rabbi Tarfon says: one may also offer oil.
2) Rabbi Tarfon said: just as we find that wine is offered as an obligation may be offered as a freewill-offering, so oil which is offered as an obligation may be offered as a freewill-offering.
3) Rabbi Akiva said to him: No, if you say so of wine it is because it is offered by itself even when offered as an obligation, can you say the same of oil which is not offered by itself when offered as an obligation?
4) Two [men] may not jointly offer one tenth [of flour for a minhah]; but they may jointly offer an olah or a shelamim, and bird sacrifices even a single bird.
Section one: According to Rabbi Akiva, while one can make a voluntary offering of wine, one cannot make a voluntary offering of just oil, without an accompanying minhah. Rabbi Tarfon holds that just as one can voluntarily offer wine on its own, so too one can voluntarily offer oil on its own.
Section two: Both Rabbi Tarfon and Rabbi Akiva agree that one can voluntarily offer wine on its own. And of course, there are situations where one is obligated to bring wine and oil to accompany sacrifices. From here Rabbi Tarfon concludes that just as wine can be brought on its own voluntarily, so too oil can be brought on its own voluntarily.
Section three: Rabbi Akiva responds by pointing out a hole in his argument. Wine is brought on its own as an obligation, when it accompanies a sacrifice. Oil, on the other hand, is always mixed in with the minhah offering. Since it is never brought on its own to fulfill an obligation, it cannot be brought on its own voluntarily.
Section four: This section is independent of the previous debate. Two people cannot jointly bring one tenth of flour for a minhah offering. However, they can jointly bring an animal sacrifice, and even jointly bring a bird. The difference between a minhah and an animal offering is derived midrashically.